The present invention relates to a process for the production of rigid polyurethane foams having a K-factor of about 0.135 BTU-in.hr.ft..sup.2 .degree.F. or less in which an HFC (hydrogen-containing fluorocarbon) in combination with a minor amount of water is used as the blowing agent.
Processes for the production of rigid polyurethane foams are known. See, for example, U.S. Pat. Nos. 3,085,085; 3,153,002; 3,222,357; and 4,430,490.
At the present time, a major concern of foam producers, particularly rigid foam producers, is the development of rigid foam systems in which the chlorofluorocarbon blowing agent is replaced with a more environmentally acceptable blowing agent. HCFCs (i.e., hydrogen containing chlorofluorocarbons), HFCs (hydrogen containing fluorocarbons), and hydrocarbons such as n-pentane cyclopentane, isopentane and blends of these blowing agents are presently considered to be possible alternatives.
U.S. Pat. No. 4,900,365, for example, teaches that a mixture of trichlorofluoromethane, a dichlorofluoroethane selected from a specified group and isopentane is useful as a blowing agent for the preparation of polyurethane foams. Dishart et al's paper entitled "The DuPont Program on Fluorocarbon Alternative Blowing Agents for Polyurethane Foams", Polyurethanes World Congress 1987, pages 59-66 discusses the investigation of various HCFCs as possible blowing agents for rigid polyurethane foams. Neither of these disclosures, however, teaches a process for the production of rigid polyurethane foams having good physical properties from polyols with an HFG blowing agent.
U.S. Pat. No. 4,972,002 discloses a process for the production of cellular plastics in which an emulsion is used as the blowing agent. A low boiling fluorinated or perfluorinated hydrocarbon or sulfur hexafluoride is emulsified in one of the starting materials from which the foam is to be produced (i.e., the isocyanate, polyol, etc.)
U.S. Pat. No. 5,169,873 discloses a process for the production of foams in which the blowing agent is a mixture of at least one fluoroalkane corresponding to a specified formula and at least one fluorinated ether corresponding to a specified formula.
U.S. Pat. No. 5,164,419 discloses a process for the production of polyurethane foams in which 1,1-difluoroethane in combination with a minimum amount of water is used as the blowing agent. However, the only foam described in this disclosure had a K-factor of 0.18 BTU-in/hr-ft.sup.2 -.degree.F.
U.S. Pat. No. 5,164,418 discloses a process for producing isocyanate-based foams in which the blowing agent is at least 10 mol % of a fluoroalkane. Mixtures of a fluoroalkane and significant amounts of water (i.e., greater than 20%) are exemplified.
U.S. Pat. No. 4,931,482 discloses the use of 1,1,1,4,4,4-hexafluorobutane as a blowing agent to produce isocyanate-based foams such as polyurethane and polyisocyanurate foams. The disclosed foams are made by reacting an isocyanate with any of the known isocyanate-reactive compounds. Water and other known blowing agents may optionally be used in combination with the required 1,1,1,4,4,4-hexafluorobutane blowing agent. The K-factors for foams produced using the hexafluorobutane blowing agent are not, however, reported.
Foams having initial K-factors below 0.135 BTU-in./hr.ft..sup.2 .degree.F. which are blown with HCFC-141b or CFC-11 are used commercially in appliance and construction applications. A process in which a polyol could be used in combination with the more environmentally acceptable HFC blowing agents to produce a rigid polyurethane foam having good physical properties, particularly a K-factor which is about 0.135 or less would, therefore, be advantageous.